1. Field of the Invention
The present invention is directed to a measuring arrangement for operating and controlling an implantable body-assist device, and in particular to such an arrangement for operating and controlling a heart pacemaker having a pacing circuit which generates pulses, and a pulse control circuit to which a measuring probe is electrically connected via a conductor in a catheter.
2. Description of the Prior Art
Measuring devices are known in the art which acquire a signal corresponding to the blood oxygen concentration of the patient in which the measuring device is implanted. Such devices are used to control the frequency of pacing of a heart pacemaker as described, for example, in German patent No. 31 52 963. The schematic structure of such a known measuring device and pacemaker is shown in FIG. 1.
In this known pacing system, a heart pacemaker H includes a combined measuring and stimulation catheter 3, and a control stage 1 alternately connects the catheter 3 to a pacing circuit 9 or to an evaluation circuit 10, which controls operation of the pacing circuit 9. Two operating conditions of the system are possible by means of the control stage 1. Given switch position 1a, the pacing circuit 9 receives an ECG signal via an electrode 6 extending through the catheter 3 and an electrode 7, which is the housing of the heart pacemaker H. The pacing circuit 9 generates a stimulation pulse via the current conductor 3a and the electrodes 6 and 7. In switch position 1b of the control stage 1, the evaluation circuit 10 receives a signal from the measuring probe 2 via the current conductors 3a and b, and generates control signals for controlling the pacing circuit 9 based on the measurement signal.
In this known system, the catheter 3 must be bipolar, at least between the control stage 1 and the measuring probe 2. Bipolar catheters, however, are thicker and corresponding less flexible, and have a higher failure rate, than single-pole catheters. Moreover, the manufacture of bipolar measuring catheters is more complicated and expensive than the manufacture of single-pole catheters.